It is generally the case that the number of functions with which vehicles in general and heavy vehicles in particular are equipped is ever-increasing. These functions are often controlled by one or more control units, or controllers, and are often intended to enhance the vehicle's passive and active safety and to render travel in it as comfortable as possible for the driver and any passengers.
The increase in the number of vehicle functions is accompanied by increasing risk of one or more functions malfunctioning. Any fault which occurs may be drawn to the driver's attention, e.g. by a warning lamp lighting up, whereupon desired measures can if necessary be taken. A malfunction may be more or less serious depending on the nature of the function concerned. For example, a fault in a function which only affects the comfort of the driver and/or passengers need not make the vehicle more difficult to drive. In contrast, a fault of a more serious kind which in some way puts at risk the safety of the driver/passengers and/or the possibility of driving the vehicle safely will need to be dealt with immediately. However, it is often both time-consuming and expensive to rescue a heavy vehicle, which makes it desirable that as far as possible the vehicle should be able independently to reach a workshop or some other suitable location even when a fault has occurred.
Heavy vehicles are therefore often capable of being put into a so-called “limp home” state whereby some functions can be switched off while the most important are kept at least partly operational so that the vehicle can passably reach a suitable location under its own power even if its maximum speed in such a limp-home state may be limited to a substantially lower speed than it can normally be driven at.
Although in many cases the limp-home state makes it possible for the vehicle to travel safely to a desired location without emergency assistance, there are also situations in which this is not possible. There is therefore a need for improved means of avoiding, for example, any need to be rescued in certain situations.
Accelerating the engine to a speed at which it will start thus makes it possible for the engine to be started despite the power train being closed, e.g. because of a fault which prevents opening of said clutch. The speed at which the engine starts may depend on the load exerted upon the engine by the closed power train. However, diesel engines in particular have a high available torque even at low engine speeds, so even with the power train closed the engine will often start at a relatively low engine speed. The invention thus makes it possible for the vehicle to continue its journey despite the clutch malfunction.
The vehicle can also be set in motion in a controlled way without behaving in a way which would be surprising to the driver, since the demand for setting in motion with the clutch closed will show that the driver is actively aware of the vehicle's behavior with the power train closed.
Further characteristics of the present invention and advantages thereof are indicated by the detailed description of embodiment examples set out below and the attached drawings.